Three unusual earthquakes that shook a suburb west of Dallas over the weekend appear to be connected to the past disposal of wastewater from local hydraulic fracturing operations, a geophysicist who has studied earthquakes in the region says.

Preliminary data from the U.S. Geological Survey (USGS) show the first quake, a magnitude 3.4, hit at 11:05 p.m. CDT on Saturday a few miles southeast of the Dallas-Fort Worth (DFW) International Airport. It was followed 4 minutes later by a 3.1-magnitude aftershock that originated nearby.

A third, magnitude-2.1 quake trailed Saturday's rumbles by just under 24 hours, touching off at 10:41 p.m. CDT on Sunday from an epicenter a couple miles east of the first, according to the USGS. The tremors set off a volley of 911 calls, according to Reuters, but no injuries have been reported.

During hydraulic fracturing, or "fracking," millions of gallons of high-pressure, chemical-laden water are pumped into an underground geologic formation (the Barnett Shale, in the case of northern Texas) to free up oil. But once fractures have been opened up in the rock and the water pressure is allowed to abate, internal pressure from the rock causes fracking fluids to rise back to the surface, becoming what the natural gas industry calls "flowback," according to the Environmental Protection Agency.

"That's dirty water you have to get rid of," said Frohlich. "One way people do that is to pump it back into the ground."

"Faults are everywhere. A lot of them are stuck, but if you pump water in there, it reduces friction and the fault slips a little," Frohlich told Life's Little Mysteries. "I can't prove that that's what happened, but it's a plausible explanation."

There are fault zones east and west of Dallas, running from there southwest through Austin all the way to San Antonio and Del Rio. Getting quakes there looks no more strange than the quakes we get in Michigan due to faults under Lake Erie off Cleveland, Ohio.

well frack my life! (sorry, couldn't resist....) Can't believe they didn't study this further FIRST, before putting it into practice. I worked in the oilfield for almost 5 years, and a lot of the work I performed was pulling up cracked casen. I always wondered in the back of my mind what it was doing to the surrounding areas, but it's pretty obvious now. Yikes!